1. Field of the Invention
The invention relates to amide derivatives of a sulfur compound in combination with a coadditive hydrocarbon as middle distillate fuel flow improvers.
2. Description of the Prior Art
Heating oils and other middle distillate petroleum fuels, e.g., diesel fuels, contain normal paraffin hydrocarbon waxes which, at low temperatures, tend to precipitate in large crystals in such a way as to set up a gel structure which causes the fuel to lose its fluidity thereby presenting difficulties in transporting the fuel through flow lines and pumps. The wax crystals that have come out of solution also tend to plug fuel lines, screens and filters. This problem has been well recognized in the past and various additives known as pour point depressants have been used to change the nature of the crystals that precipitate from the fuel oil, thereby reducing the tendency of the wax crystals to set into a gel.
It is known in the prior art to employ various polymeric and copolymeric materials as pour point depressants for controlling wax deposition of wax-containing petroleum fractions, e.g. U.S. Pat. No. 3,600,311 teaches that branched alkylene polymers having a molecular weight of about 1,000 to 50,000 and with 10-55% branching, e.g. hydrogenated polybutadiene, can be used to improve the cold flow characteristics of middle distillate fuels.
Recently, it has become known that pour point depression alone is not a sufficient phenomenon to alleviate some problems caused by wax crystals in various fuels, especially middle distillates. In those petroleum fractions, it has been observed that the wax crystals formed in the presence of the pour point depressant are often too large to enable the wax-cloudy fuels to pass easily through screens and orifices commonly encountered in the equipment employed either in distribution or in use of such fuels. This problem has been alleviated by the addition to said fraction of petroleum products of wax crystal modifiers which are referred to as flow and filterability improvers.
U.S. Pat. No. 3,961,916 teaches that the low temperature flow characteristics of petroleum middle distillates can be very satisfactorily controlled by the proper choice of a combination of a nucleating agent or wax growth stimulator and a wax crystal growth arrester.
Other additive combinations have been taught for modifying the cold flow characteristics of petroleum fuels including:
U.S. Pat. No. 3,846,093 teaches modifying the low temperature filterability of middle distillate fuels by the addition of an amorphous hydrocarbon and an N-aliphatic hydrocarbyl succinamic acid or derivative thereof; and, U.S. Pat. No. 4,014,663 teaches a synergistic mixture based on the combination of a hydrocarbon which is a derivative of an alphaolefin and said succinamic acid or derivative thereof.